This invention relates to surface acoustic wave (SAW) devices and especially to a SAW device that is magnetically tuned.
SAW devices intrinsically have a fixed delay the amount of which is determined by material constraints and the physical separation between input and output terminals. In most present applications, any deviation from this fixed delay is achieved by placing a series of fixed taps between the input and the output to obtain a stepwise variable delay. A few techniques have been proposed for obtaining continuously variable delays with SAW devices but these have a number of limitations. For example: (a) Mechanically variable devices are quite difficult to fabricate and the delay changes can be made only very slowly; (b) A technique involving dispersive delay lines can be used to achieve large variable delays but it involves a highly complex system and suffers from high insertion loss.
An electronically variable phase shift can be obtained by making use of phonon-electron interactions in a piezo-electric semi-conductor or adjacent semiconductor and piezo-electric materials. However, such devices involve specialized configurations and are thus not adaptable to many standard SAW devices.
An object of the present invention is to vary the delay and phase shift of an SAW device electrically so that rapid and continuous changes in delay and phase shift are provided.
Another object is to provide a simple SAW device in which such changes are possible.
A further object is to provide such a SAW device which also has a small insertion loss.
Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings wherein: